A major feature of rupture-prone "vulnerable" atheromata is macrophage (Mf) death, which leads to plaque necrosis. Mf death, plaque necrosis, and coronary artery disease (CAD) are accelerated in insulin-resistant states, including metabolic syndrome and type 2 diabetes. However,a precise understanding of how insulin resistance promotes advanced atherosclerosis at the cellular and molecular levels is lacking. The overall objective of this proposal, within the context of the PPG, is to help shed new light in this critical area. Using free cholesterol (FC)-loaded Mfs as a model of advanced lesional Mf death, the Rl has elucidated a unique multi-hit mechanism of Mf apoptosis that involves at least 3 components: the ER stress pathway known as the Unfolded Protein Response (UPR);the MAP kinase JNK;and a newly discovered pathway involving the functional interaction of the type A scavenger receptor (SRA) and toll-like receptor 4 (TLR4). Importantly, the three Rl's'of the PPG have shown that insulin-resistant Mfs have increased SRA expression and increased susceptibility to SRA/ER stress-induced death both in vitro and in vivo. In another set of experiments, the Rl found that the adipokine adiponectin, which is reduced in insulin-resistance and CAD, suppresses FC- induced UPR activation and apoptosis in Mfs.Thus, the decrease in adiponectin in insulin resistance may represent another molecular-cellular link to plaque progression. With this background, Aim IA will explore the hypothesis that a unique functional interaction between SRA and TLR4 in ER-stressed Mfs triggers apoptosis. In collaboration with the other projects, we will then investigate how insulin resistance in Mfs affects the SRA/TLR4apoptosis pathway. In Aim IB, we will test the hypothesis that deficiency of Mf-SRA and TLR4 decreases late lesional Mf apoptosis and plaque necrosis in Ldlr-/- mice, especially in the setting of Mf insuljn resistance. Aim HAwill elucidate the mechanisms of how adiponectin suppressesthe UPR and Mf death in ER-stressedwild-type and insulin-resistant Mfs. In Aim MB, we will test the hypotheses that adiponectin deficiency enhances UPR activation, Mf death, and plaque necrosis in advanced lesions of adiponectin-deficient Ldlr-/- mice and that adiponectin excess suppresses these parameters. Thus, through extensive interactions among the 3 Rl's and the Lesion Analysis Core, this project will explore potential molecular-cellular links between insulin resistance and the advanced progression of atherosclerotic lesions.